FLUOEINE. 265 



potassium fluoride, Fremy made use of it at once as a source of the 

 pure, dry acid. 



He thus obtained a compound which was gaseous at ordinary temper- 

 atures, and which condensed in a freezing mixture to a colorless liquid 

 having a great affinity for water. Here, then, is a reaction of great 

 importance — the preparation of hydrofluoric acid in a state of purity. 



Allow me to remark incidentally that when Humphry Davy elec- 

 trolyzed concentrated hydrofluoric acid tlie badly conducting liquid 

 which he obtained at the end of his experiment was the acid very 

 nearly anhydrous. 



The second fact, which, as I have said, was almost unnoticed, and 

 which has been of great interest to me, especially at the end of my 

 researches, was that fluorine has the greatest tendency to unite with 

 nearly all compounds to form addition products. 



In brief, fluorine easily forms ternary and quaternary compounds. 

 Let chlorine act upon a fluoride, instead of isolating fluorine we shall 

 prepare a fluochloride. Employ oxygen, and we shall make an oxy- 

 fluoride. This property explains to us the failures of Louyet, of the 

 brothers Knox, and of other experimenters. Even when dealing with 

 dry fluorides in an atmosphere of chlorine, bromine, or iodine we shall 

 obtain ternary compounds instead of tree fluorine. This fact was 

 clearly established by Fremy. His memoir covers so great a number 

 of experiments that it seems to have discouraged chemists, to have 

 stopped further attempts. Since 1856, the date of publication of 

 Fremy's memoir, researches upon hydrofluoric acid and the isolation of 

 fluorine have been few. The question seems to have been in a state of 

 arrested development. Nevertheless, in 1869, Gore took up method- 

 ically the study of hydrofluoric acid. He started with the anhydrous 

 acid prepared by Fremy's method. He determined its boiling point, the 

 tension of its vapor at difierent temijeratures ; indeed, all of its prin- 

 cipal properties. FJis memoir is one of remarkable exactitude. Among 

 the numerous investigations of Gore we will consider for the moment 

 only the following, to which I beg your attention: 



In a special apparatus this chemist electrolyzed anhydrous hydro- 

 fluoric acid containing a little fluoride of platinum in such manner 

 that the gases x)roduced could be collected at each electrode. At the 

 negative pole he saw hydrogen disengaged abundantly, while the rod 

 Avhich terminated the positive pole was rapidly corroded. This phe- 

 nomenon was identical with that observed by Faraday during the elec- 

 trolysis of calcium fluoride. Gore next verified the observation of 

 Faraday, that hydrofluoric acid containing water allows the current to 

 pass, but that the absolutely pure anhydrous acid is a nonconductor. 

 In one of his experiments Gore tried to electrolyze a hydrofluoric acid, 

 which, because of an impurity, was a good conductor; and, seeking to 

 avoid the wasting of the electrode, replaced the latter by a stick of 

 carbon. 



